"Astrophysics."

"That might explain it. Second specialty?"

"Astrogation." He couldn't resist adding, "That's more advanced than the
simple space navigation you use, Commander."

O'Brine started to retort, then apparently thought better of it. "I hope
you'll be able to carry out your orders, Lieutenant," he said stiffly.
"I hope, but not much. I don't think you can."

Rip asked, "What are my orders, sir?"

O'Brine waved in the general direction of the wall. "Out there somewhere
in the asteroid belt, Foster, there is a little chunk of matter about one
thousand yards in diameter. A very minor planet. We know its approximate
coordinates as of two days ago, but we don't know much else. It happens
to be a very important minor planet."

Rip waited, intent on the commander's words.

"It's important," O'Brine continued, "because it happens to be pure
thorium."

Rip gasped. Thorium! The rare, radioactive element just below uranium in
the periodic table of the elements, the element used to power this very
ship! "What a find!" he said in a hushed voice. No wonder the job was
Federation priority A, with Space Council security! "What do I do about
it?" he asked.